Wind power has attracted much attention during recent years as an alternative source of energy. Wind turbines are used to convert kinetic wind energy into electric power. For this purpose, utility-class wind turbines have wind rotors which are usually equipped with three rotor blades to extract kinetic energy from the wind. Nevertheless, it must be possible to keep the rotor of a wind turbine in position when it is at a standstill. Arresting the rotor is important for servicing and repair. Apart from the necessity to lock the rotor, it is also necessary to reduce the rotor speed at least within a certain range by means of a mechanical brake. This is commonly realized by disc-breaks. For safety reasons, the functioning of the brakes has to be tested within predetermined time intervals during the operation of the wind turbine.
For testing the brakes as known in the art, a switch off of the wind turbine is necessary. This means a down time for the turbine and a decrease of the energy yield.